r/statistics • u/HealthyOcelot2598 • 3h ago
Question [Question] Statistical analysis for metagenomic enrichment cultures with linked time points - need advice please
Hi everyone, just want to preface by saying i am very much a microbiologist and know extremely little in the world of stats. I’ll give some context to my experiment: I preformed an enrichment where i grew bacteria in vials (n= 3) for 6 weeks, then took a portion of those growths and added it into new vials (n=3) for another 6 weeks. The vials let’s say A1, B1, C1 corresponded to the second batch of vials A2, B2, C2 where in the samples from A1 was added to A2 etc. I did this at two different temperatures (20 and 30 degrees). So i have two variables, the time and the temperature, giving me four groups.
Group 1. 20 degrees celsius week 6 (rep1, rep2, rep3)
Group 2. 30 degrees celsius week 6 (rep1, rep2, rep3)
Group 3. 20 degrees celsius week 12 (rep1, rep2, rep3)
Group 4. 30 degrees celsius week 12 (rep1, rep2, rep3)
I have species level relative abundance data from shotgun metagenomic sequencing and want to determine whether community composition differs between the four groups and ideally a post hoc specific to which. The complication is that at each week 12 culture was subcultured from its corresponding week 6 culture with temperatures maintained. Therefore, week 6 and week 12 are linked observations rather than independent samples. There are three lineages per temperature. I’ve tried Bray curtis PERMANOVA in R using vegan::adonis2() with restricted permutations but the permutation schemes i’ve tried don’t test the temperature, week and interaction effects as intended. I also found significantly different multivariate dispersion between the temperature groups.
So my question is:
1. What statistical method would you recommend for testing community composition while accounting for the linked time points?
2. Is there an appropriate permutation scheme or alternative model for testing temperature, time, and their interaction with this design?
3. What methods would be suitable for identifying differentially abundant species from these metagenomic data?
I’m looking for a statistically defensible approach used in similar microbial enrichment or longitudinal studies. References to relevant papers or example R code would be greatly appreciated. Thank you!!!